When large composite components, such as those components used in the manufacture of wind turbine blades are assembled, there is often the problem that stress concentrations can be created in the joint region. For example, in a wind turbine blade, the structural spar section may be up to 50 m in length and have a width of up to 2 meters. Such a spar may be formed in a box configuration from four components, two spar caps separated by two shear webs. The individual composite components are pre-made, that is they are cured composite components and therefore stiff.
Due to the large size of the composite components involved, each individual composite component can be difficult and expensive to mould accurately enough for future accurate assembly. For instance, in a manufacturing plant having a production line, many moulds may be used to fabricate the same composite component. However, there may be variations between the different moulds such that when the composite components are to be assembled they are not all identical. This can result in a less accurate fit at a joint, with variations in three spatial dimensions.
It is known in the prior art to overcome the above issues by filling up the gaps between the composite components to be joined by using an adhesive as a filler. However, this process results in an unpredictable adhesive usage which may result in the joint having a reduced strength.
It is also known in the prior art to assemble the composite components together and apply a clamping force so that the components are forced together. The clamping force removes any gaps that may exist between the two components and thus results in uniform adhesive usage. However, this approach creates a preload at the joint as each composite component will tend to try to deform to its original shape. These preloads result in residual stresses which may structurally weaken the joint.
It is an aim of the present invention to create a composite joint which does not create residual stresses and which can have a uniform and pre-determined adhesive usage.